Variable resistance device



Oct. 9, 1956 v. CRADDOCK, v 2,766,359 VARIABLE RESISTANCE DEVICE Filed Jan. 16, 1955 2 Sheets-Shem} 1 6. l4 CRADDOCK G. v. CRADDOCK 2,766,359 VARIABLE RESISTANCE DEVICE Filed Jan. 16, 1953 2 Sheets-Sheet 2 F/G IQ 4 m/vixvron M CPADCK United States Patent VARIABLE RESISTANCE DEVICE Gerald V. Craddock, West Newbury, Mass., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application January 16, 1953, Serial No. 331,698

7 Claims. (Cl. 201-55) This invention relates to a variable resistance device utilizing an annular resistance element and the general object of this invention is to provide such a device of simple and inexpensive design.

According to the general features of the invention, this object is attained by mounting an annular resistance element and a collector ring in spaced parallel relation in a case through which a control shaft of insulating material extends. The inner end portion of the shaft is of rhombic or other non-circular cross-section and carries a formed spring member having arms deflected to make sliding connection between the resistance element and the ring. The deflection of the arms deforms the central part of the spring member thereby locking it to the shaft.

These and other features of the invention will be understood from the following detailed description taken in conjunction with the accompanying drawing in which:

Fig. 1 is a partially sectionalized, side elevational view of one form of variable resistance device according to the invention;

Fig. 2 is a view of the device of Fig. 1 along the plane A-A;

Figs. 3 and 4 are partial side elevational and bottom plan views, respectively, of the shell of the device of Fig. 1;

Fig. 5 is an isometric view of the shaft of the device of Fig. 1;

Fig. 6 is a top plan view of the spring member of the device of Fig. 1;

Fig. 7 is a partially 'sectionalized, side elevational view of a variable resistance device according to the invention utilizing a disc annular resistance element;

Fig. 8 is a partial view of the device of Fig. 7 along the plane B-B;

Fig. 9 is a top plan view of the spring member of the device of Fig. 7; and

Fig. 10 is a cross-sectional, side elevational view of a dual variable resistance device according to the invention.

Referring now to the drawing, Figs. 1 through 6 show principal parts and an assembly drawing of one type of variable resistance device according to the invention. A molded nylon case 1 is provided with an integral threaded mounting boss 3 surrounding and forming a bearing for a control shaft 4. The control shaft 4 is made of insulating material, preferably nylon, and is provided with a cylindrical bearing portion 5, a bearing shoulder 6 and a diamond shaped portion 7. A screw driver slot 8 is provided for turning the shaft.

A ring shaped resistance element 9 which may be deposited carbon or any conventional resistor element, such as wire wound or carbon composition, is supported by, or attached to, insulator 10. Insulator 10 is fastened in the case 1 and terminals 11 and 12, which are positioned in slots 13 and 14 respectively, provided in case 1, are held in contact with the ends of the resistance element 9 by a single screw 15.

A formed conductive spring member 16, having a too diamond shaped cut-out 17 for mounting on the diamond shaped portion 7 of the shaft 4, is provided for making connection between a resistance element soft carbon contact brush 20 and a one piece collector ring and terminal 18 through a contact brush arm 19, and collector ring contacting arms 21 and 22. The pressure of the spring on the contact areas deforms the central part of the spring to lock it to the shaft.

The single piece collector ring and terminal 18 is held in a recess provided in a molded plastic disc 24 by the pressure of the contact spring arms 21 and 22, the disc 24 being inserted into the bottom of the case 1 and secured thereto by screws 25 and 26.

In the variable resistance device of Fig. 7, a disc annular carbon resistance element 27, deposited on insulator 28, is utilized. In this embodiment, the contact spring 29 difiers in design from the contact spring 16 used with the device of Fig. 1 wherein a ring shaped resistance element 9 is utilized, in that the carbon contact brush 31 must make slidable contact with a surface perpendicular to, instead of parallel with, the axis of the shaft 4. The functions of the spring, however, are identical with those of the spring of Fig. 1. Again a single screw 32 is utilized for the dual purpose of holding the insulator 28 in position in the case 33 and for holding the terminals 23 and 34, which are positioned in slots provided in the case 33, in contact with the ends of the resistance element 27. Here, however, an insulating washer 35 must be used.

The principal features of the invention are particularly well adapted to multiple resistance element devices, a typical illustration of which is disclosed in the dual element device of Fig. 10. In this device the molded case 36 houses a molded insulating disc 37 having recesses on both sides thereof for collector rings 42 and 43, the terminal portions of which pass through slots provided in the case 36, two resistance elements 38 and 39 and their associated insulators 40 and 41, respectively.

The shaft 44 is similar to the shaft 4 of Fig. 1, however, the diamond shape portion 45 is sufficiently long to support the two contact springs 46 and 47. The insulator 41 is a solid disc fitting within and sealing the open end of the case 36.

While the invention has been described with respect to particular embodiments for 'purposesof illustration, it will be understood that the devices could be modified in various ways in accordance with the general principles of the invention and the requirements of the particular conditions of use. For example, the case may be made" of metal to provide greater heat dissipation, or the spring supporting portion of the shaft could have a variety of diiferent non-circular cross-sectional shapes, or the terminal members for the resistance elements could be connected thereto in any conventional manner, or either or both disc or ring type resistance elements could be utilized in multiple element units. These and numerous other arrangements may be devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. In a variable resistance device, a case, an annular resistance unit and a collector ring mounted in the case in spaced parallel relation, a control shaft of insulating material mounted in the case with its axis normal to the plane of the ring and having a portion of non-circular cross-section between the unit and the ring, a brush for the unit and means for making a sliding electrical connection between the ring and the brush comprising a spring member having a hole therethrough for mounting the member on the non-circular portion of the shaft and having opposed arms in pressure contact with the brush and the ring, the stressing of the arms for making the 3 pressure contact deforming the spring to lock it on the shaft.

2. In a variable resistance device, a control shaft of insulating material with a cylindrical bearing portion and a second portion of non-circular cross-section, a molded case with an integral threaded mounting boss surrounding and forming a bearing for the shaft, an annular resistance unit and a collector ring mounted in the case in spaced parallel relation in planes normal to the axis of the shaft, a contact brush for the unit and means for making a sliding electrical connection between the l and the brush comprising a spring having a hole therethrough for mounting the spring on the non-circular portion of the shaft and having opposed arms in pressure contact with the brush and the ring, the stressing of. the arms for making the pressure contact deforming the spring to lock it on the shaft.

3. In a variable resistance device, a case, an annular resistance unit and a collector ring mounted in the case in spaced parallel relation, a control shaft of insulating material mounted in the case with its axis normal to the plane of the ring and having a portion of non-circular cross-section between the unit and the ring, a brush for the unit, a spring member having a hole there-through for receiving the non-circular portion of the shaft and opposed arms on the spring for making pressure contact with the brush and the ring for making a sliding electrical connection between the ring and the brush, the stressing of the arms for making the pressure contact deforming the spring to lock it rigidly to the non-circular portion of the shaft.

4. In a variable resistance device, a case, an annular resistance unit and a collector ring mounted in the case in spaced parallel relation, a nylon control shaft mounted in the case with its axis normal to the plane of the ring and having a portion of diamond shaped cross-section between the unit and the ring, a brush for the unit and means for making a sliding electrical connection between the ring and the brush comprising a spring member having a hole therethrough for receivingthe diamond shaped portion of the shaft and having opposed arms in pressure contact with the brush and the ring, the deformation of the spring due to the stressing of the arms for making the pressure contact locking the spring rigidly to the shaft.

5. In a variable resistance device, a case, an annular resistance unit and a collector ring mounted in the case in spaced parallel relation, 2. pair of terminal members for the resistance unit, a control shaft of insulating material mounted in the case with its axis normal to the plane of the ring and having a portion of non-circular cross-section between the unit and the ring, a brush for the unit, means for making a sliding electrical connection between the ring and the brush comprising a spring member mounted on the non-circular portion of the shaft and having opposed arms in pressure contact with the brush and the ring and a single screw supporting the resistance unit in the case and holding the terminals in contact with the resistance unit.

6. In a variable resistance device, a case, a recessed insulating disc mounted in the case, a one piece collector ring and terminal member positioned in the recess on the disc, an annular resistance unit mounted in the case in spaced parallel relation with the ring, a control shaft of insulating material mounted in the case with its axis normal to the plane of the ring and having a portion of non-circular cross-section between the unit and the ring, a brush for the unit and means for making a sliding electrical connection between the ring and the brush comprising a spring member having a hole therethrough for receiving the non-circular cross-section of the shaft and having opposed arms in pressure contact with the brush and the ring, the ring and terminal mem er being held in the recess of the disc soleiy by the pressure of the contact spring, the stressing of the arms for making the pressure contact deforming the spring member to lock it on the shaft.

7. In a multiple variable resistance device, a case, a plurality of annular resistance units each having a corresponding collector ring, said units and rings being mounted in the case in pairs and in spaced parallel relation, a control shaft of insulating material mounted in the case with its axis normal to the planes of the rings and having a portion of non-circular cross-section, brush for each unit and means for making a sliding electrical connection between each ring and its correspondin brush comprising a spring member having a hole therethrough for receiving the non-circular portion of the shaft between the ring and resistance unit of each pair, and each spring having opposed arms in pressure contact with its brush and corresponding ring, the stressing of the arms for making the pressure contact deforming the spring members to lock them rigidly to the shaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,934,228 I-Iill Nov. 7, 1933 2,177,290 Schellenger c. Oct. 24, 1939 2,572,651 Mucher Oct. 23, 1951 FOREIGN PATENTS 250,766 Great Britain Apr. 22, 1926 

